Such a pressure welding machine is known in the form of a double-head friction welding machine from EP 0 246 239 B1. It comprises a frame with a machine bed, at which two friction welding heads are mounted in such a way that they are movable in opposite directions along a common feed axis. They are moved by two adjusting units with feed drives along the feed axis. The adjusting units are mounted adjustably at the machine frame and are fixed individually in the desired position at the machine bed by hydraulically actuated friction brakes. A central workpiece is connected to additional workpieces on both sides by friction welding with the double-head friction welding machine. The spindle rotations of the two friction welding heads are synchronized by a common countershaft provided with a motor and a brake. Different workpiece lengths result in different path lengths for the friction feed and the upsetting feed, which are generated by different lengths of extension of the feed drives. To absorb the upsetting forces during friction welding, which amount to several tons, the pressure welding machine has a massive frame and machine bed. This means a great design effort, and undesired deformations nevertheless cannot be absorbed. On the other hand, the accessibility of the workplace is limited by the large frame construction.
EP 0 059 544 A1 shows another friction welding machine with spindles that are likewise synchronized by means of a countershaft. The adjusting units are fixed here rigidly and unmovably to the machine bed.